Space-charge tube



y 1950 w. s. BRIAN 2,506,265

' SPACE-CHARGE TUBE Filed Jan. 6, 1948 HNODE 14 $CREEN GRID f3 047/1005 f0 o/vrRoL GRID 72 5240s a/lq/ese GR/D f/ 5/0540 R005 1 CONTROL GRID IZ/ 77 seems/v 62/0 73 I 5 fl/VODE f4 /3 i A? f3 5 /3 I /Z I T '3 1 1 1/ I I y INVENTOR VV/LLI/IM IS. BRm/v m g M ATTORNEY Patented May 2, 1950 liTE D STATE T OFF ICE SPACE-CHARGE'TUBE William S. Brian; Great Neck, N. .,,;assignor to Hanson-Gorrill-Brian. Incl, Glen Cove, N. Y a corporation .of New York.

Application January 6, *1948', Serial-No. 693

-,5:Glai ms. 1

This invention relates tovacuum tubes, and more particularly to vacuum tubes utilizing" a space-charge grid.

The use of the first grid oi'a multi-grid vacuum :tube as a so-called' "space-charge grid," to overcome the space-charge surrounding the electron emitter and consequently lower the internal resistance of the tube, has been known for-many years. This result is achieved by operating the first grid at a positive potential with respect to the cathode or other-electron emitting element in .the vacuum tube. However, the first grid in standard tubes isphysica'lly so close to thecathode that it draws excessive current when it is operated with enough positive voltage to perform its function as a space charge grid satisfactorily. Because of'=this defect with conventional tubes their use as space-charge grid tubes ing the cathode that it can be operated with suflicient positive voltage on the space-charge grid without drawing excessive current.

A further object of the present invention is :to provide means for constructing a virtual cathode having a large area without consuming an excessive amount of'power.

A still further object ofthe present invention is to decrease the internal resistance of the tube by efliciently overcoming the space charge surrounding the electron emitter.

'Stillanother object is to provide a novel vacuum tube especially useful as an-audioirequency amplifier, producing a minimum amount of distortion.

A further object of the .present invention isv to provide a. circuit-Tor utilizing the-advantages :of :such a tube and minimize the change inthe tubes 'transconductancedue to change in grid bias.

"These and other advantageous, objectsare robs tained in a.tube.:-bu.i1tv :in accordance with the present 'invention by providing a plurality of shield orelectron :defiectingrods interposed between the cathode or other electron emittin surface and the members supporting the first. or space-charge grid. Since :this grid is operated at a positive potential with respect to "the cathode, the electronsemittedfrom :the cathode are attracted thereto. However, a great. many such electrons strike the. members supporting.

Cal

or inner-most grid. 1' I.

z, the. grid structure and are conducted away in the :form of grid current. Such current not only isqundesirable in that it causes excessive-v heatingwof' :the grid, but-:itacauses the tube to beineificient and uneconomical to operate.

By providing, shield rods between the cathode and the grid, the path of the emitted electrons may be directed so. that. a reat percentage of them "pass-between the interstices of the spacecharge grid structure and a minimum number strike the grid supporting members.

The operation of the present invention will become more apparent from the following detailed description of the tube structure and 0p- .eration ;,t aken inconnection with the drawings wherein:

.Fig. 1 is a cutaway view of one type of electron :tube constructed in accordance with the .present invention;

Fig. 2 is a cross-section of the tube shown in Fig. ;1 taken on the "line 2-2 ,of Fig. 1; and

Fig. 3 is aschematic circuit showing the tube connected as :a voltage .amplifier.

Referring now more particularly to Fig. :1; which shows a cutaway of a tube constructed in accordance-withtheepresent invention. Rod- -like cathode Hi can be seen to be surrounded ;by a set of three coaxial grids H, 12 and H which may be of thexhelical-type. Each of these gridsiis supportedxrespectively by rod-like mem bers ii I, 1 2, and I3 oriented parallel-to cathode I'O. Shield rods 1:! can be seen mounted :parallel to the cathode 10 and positioned between it-and rod-like members l'l supporting the first Conventional cylindrical anode 1M surrounds the grid and cathode structure, andzthe whole assembly is supported with- ";in metallic envelope -15. The lead-in wires to the various elements are connected to their respective/pins Jtqat the base of the tube structure. Althou h, th emb dimen shown. infi iszoithc screcneri ct pe tub havin a metal- 5H0 envelope. the invention :may', of cours be applied to tubes havin a di ferent number of electrod s andutilizrin envel p -mad of glass- Fi -22 showsa cro.ss: .eotion;-of the tube shown in fi -.1. :As: in Fi .1, i anbeseenthat oathrode. iuheated byaheater 2:2 is surrounded by grids H, =12 and i 13. !lihese rid are sh wn to the oval. in cross-section which permits of grea .mechanical: rigidity, although they might easily 3 in a plane with cathode l and another supporting member Hi. In this same plane, shield rods I! may be seen interposed between cathode ID and grid H.

In operation, first grid H is made positive with respect to cathode IS. Its effect is thus to counteract the effect of the negative space charge which surrounds an electron emitter such as cathode i8 and to produce a cloud of electrons at the plane of the first grid. This cloud acts as a virtual cathode. tube is similar to that of a tetrode having a-large effective cathode area behaving as if it were temperature limited. Grid I2 is used as the control or signal grid and grid I3 is operated as a screen grid. Although no suppressor grid is shown, such a grid may be used to prevent' the secondary electrons from anode I4 from re turning to grid l3.

To reduce the space-charge grid current, the t'wo side rods or shield members i? are utilized. "These-rods or members I! could be electrically --connected to either the cathode it or the control grid i2. By thus restricting the path of electrons to the vicinity of the lateral wires of the space-charge grid H, its current is considerably {reduced with the resultant increase in efficiency. The magnitude of this increased efficiency is considerable since the area of supporting rods H which would intercept emitted electrons is greater than the combined area of all the useful field- J'producing lateral wires of grid H. Thus, the total-current of the'space-charge grid i l is greatly reduced by the utilization of shield'rods or me'mbers l1 without in any way damaging the electrical performance of the tube.

-'.-Fig. 3 shows the tube of Figs. 1 and 2 in a schematic form connected in a voltage amplifier circuit. An alternating input signal is applied "to control grid I2 through coupling condenser 20. Resistor 21 is connected between control grid [2 and ground. Cathode I0 is heated by heater 22 which has a source of potential 23 applied to [heater leads 24 and 25. Cathode bias resistor l 26 is connected between cathode ill and ground,

j and is by-passed in conventional manner by cathode by-pass condenser 21.

Anode i4 is con- "nected to 13+ through plate load resistor 28.

Resistor 29 connected between B+ and screen grid i3, and by-pass condenser 30 connected between screen grid l3 and ground serve as a con- "ventional screen grid' supply filter. Positive voltage is applied to space-charge grid H through voltage dropping resistor 3! connected to B+.

Shield rods H are conductively connected together and in turn are connected to control grid l2. Condenser 32 serves to couple the amplified signal from the plate end of plate load resistor f 28 to the succeeding stage.

It will be noted that the voltage for the spacecharge grid 1 l is'reduced. This causes greater than normal reduction inthe plate current re- 'sulting in an increased transconductance in the negative bias region. When the control grid I2 is made less negative, that is, when the control grid bias is made less negative, thespace-charge 'igrld current is decreased. This decrease causes 1 less voltage drop across resistor 31 thereby in- The operation of such a" efficient manner.

is utilized in a circuit such as described, the

creasing the positive voltage on space-charge grid H and increasing the plate current. Thus, the result of such operation is to reduce distortion resulting from a change in transconductance with changing grid bias.

From the above it will be seen that a tube built in accordance with the teachings of my invention results in a tube. having an extremely low internal resistance. By the use of the shield rods, as described, this advantage is achieved in an Furthermore, if such a tube change in tube transconductance due to a change "in grid bias is minimized thereby resulting in distortion reduction.

Since many changes could be made in the above construction and many apparently widely difierent embodiments of this invention could be made without departure from the scope thereof, it is intended that all matter contained in the above description or-shown in the accompanying drawings shall be interpreted as surrounding said screen grid, and a pairof shield rods positioned between said space-charge grid and said cathode, a source of potential having its negative terminal grounded, a first impedance element connected between the positive terminal .of said source of potential and said space-charge grid, 9. second impedance element connected between said positive terminal and said screen grid,

.a third impedance element connected between said positive terminal and said anode, a fourth impedance element connected between said control grid and ground, and a conductive connec- =tion between said control grid and said shield rods, said impedance elements cooperating with said shield rods in use to minim ze changes in tube transconductance with changes in operating grid'bias.

2. An electronic circuit comprising an electron ,tube having a cathode, a plurality of accelerating grids, a control grid, an anode, and a plurality of electron repelling members surrounding said cathode, a plurality of resistances, a source of potential having its negative terminal grounded and its positive terminal connected through a respective one of said resistances to said plurality of accelerating grids, and a conductive connection between said electron repelling members and said control grid, said resistances operating in conjunction with said repelling members to minimize changes in tube transconductance with changes in operating grid bias.

3. An electronic circuit comprising, an electron tube comprising a cathode, a space-charge. grid surrounding said cathode, shield rods located. between said cathode and said space-charge grid, a control grid surrounding said. space-charge. grid and an anode surrounding said control grid, a

source of potential connected to said anode; and impedance .elements connected. between said source of voltage, the anode and said spacecharge grid, said impedance elements serving in conjunction with said shield rods to minimize changes in tube transconductance due to changes in bias of said control grid.

4. An electron tube comprising a cathode, a positive grid surrounding said cathode, said positive grid having supporting members, shield members interposed between said cathode and said grid supporting members for reducing the spacecharge grid current of the tube, a control grid. surrounding said positive grid, said positive grid serving in use to counteract the efieot of the negative space charge surrounding the cathode by producing a region of positive charge around the latter, and an anode surrounding said control rid.

5. An electron tube comprising a cathode, a positive helical grid surrounding said cathode, said positive grid having supporting rods, a pair ofshield rods interposed between said cathode and said supporting rods for reducing the spacecharge grid current of the tube, a helical control grid surrounding said positive grid, said positive grid serving in use to counteract the efiect of the negative space charge surrounding the cathode by producing a region of positive charge this serving as a virtual cathode, a screen grid surrounding 6 said control grid and an anode surrounding said screen grid.

WILLIAM S. BRIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,118,922 Haines et al. May 31, 1938 2,148,266 Haines -1 Feb. 21, 1939 2,156,079 Heggs Apr. 25, 1939 2,203,221 Jonker et a1 June 4, 1940 2,285,498 Herold Mar. 18, 1941 2,441,254 Stromeyer May 11, 1948 FOREIGN PATENTS Number Country Date 498,167 Great Britain Jan. 4, 1939 

